Method of preparing vinyl halide polymers and copolymers with polyolefins

ABSTRACT

Polymers of excellent impact strength, reduced particle size, and enhanced proportions of fines are obtained in the bulk polymerization of a vinyl halide or mixture thereof with comonomer(s) in the presence of a high molecular weight polyolefin added to the polymerization mass upon conversion of 0 to about 20% by weight of monomer(s) to polymer, by removing from the polymerization mass during the thick paste state thereof sufficient vinyl halide to adjust the effective concentration of polyolefin to above about 3.5% based on vinyl halide. The resultant product which contains an enhanced proportion of fines and is devoid of massive agglomerates, requires less mechanical work in comminution or shorter heating in melting in subsequent conventional processing steps.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of copending application Ser. No.746,048, filed Nov. 30, 1976 now U.S. Pat. No. 4,067,928, which is acontinuation-in-part of application Ser. No. 541,163 filed Jan. 15,1975, now U.S. Pat. No. 4,007,235.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improvement in the preparation of polymersof high impact strength and enhanced processability. More particularlythe invention relates to an improvement in the bulk polymerization ofvinyl halide or vinyl halide-comonomer mixtures in the presence of highconcentrations of high molecular weight polyolefins. It is especiallyconcerned with a novel improvement in said polymerization whichdiminishes formation of product agglomerates and provides a more finelydivided, more homogeneous, and more easily processed particulatepolymer.

2. Description of the Prior Art

It is known to polymerize a vinyl halide, e.g. vinyl chloride, or up toabout 50 weight percent of mixture thereof with a compatible comonomerin bulk in the presence of a polyolefin to obtain a vinyl halide polymerof improved impact strength and processibility. Thus, according tocopending U.S. application Ser. No. 746,046 filed Nov. 30, 1976, of A.Takahashi which is a continuation-in-part of copending U.S. applicationSer. No. 674,202, filed Apr. 5, 1976 now U.S. Pat. No. 4,071,582, which,in turn, is a continuation-in-part of U.S. application Ser. No. 427,895,now abandoned, filed Dec. 26, 1973, as a continuation-in-part of Ser.No. 251,099 filed May 8, 1972, now abandoned, vinyl halide or a vinylhalide-comonomer mixture can be polymerized in a single or two stagebulk reaction in the presence of about 0.05 to about 20% of a polyolefinrubber of weight molecular weight ranging from about 50,000 to 1,000,000or higher to produce a polyvinyl halide product containing both free,i.e. dispersed, and grafted polyolefin of excellent impact strength, andother desirable properties such as reduced melt viscosity. It is nowfound, however, that polymers of especially excellent high impactstrengths of the order of about 10 to 20 foot-pounds per inch orgreater, are obtained as a general result in the reference process whenthe amount of polyolefin charged is above about 3.5 weight percent,preferably above about 5.3 weight percent based on the vinyl halideconcentration. However, it is also found that use of such highconcentrations of polyolefin, especially of polyolefins of molecularweight above 150,000 incurs difficulties in mixing the reaction mass,and results in a product having a relatively low proportion of finelydivided particles and a substantial number of relatively massive lumpsor agglomerates. In the reference polymerization, as soon as theagitated reaction mixture is warmed up to initiate polymerization, thepolymerization mass proceeds from a substantially clear solution ordispersion of polyolefin in vinyl halide or vinyl halide-comonomermixture to a milky, opaque emulsion. After about one hour, the reactionbecomes a paste, and after about 1.5 hours of reaction, corresponding toabout 25 to 30% conversion of vinyl halide to polymer, the reactionisotherm shows a rapid increase, with concurrent thickening of thepaste, i.e. development of a "thick paste state" in the reaction mass.After about 40 to 45% conversion of the vinyl halide monomer to polymer,the thick paste becomes, in the main, a fine non-viscous powder. Whenhigh concentrations of polyolefin are charged to the reaction in orderto obtain the aforementioned polymer of exceptionably good impactstrength, the thick paste state of the reaction mixture is so viscous,i.e. of consistency substantially similar to unbaked dough, that theagitation of the mixture provides little mixing effect in thepolymerization mass. In other words, the reaction mixture consists ofseveral large dough-like agglomerates, or in extreme cases, a singledough-like lump, adhering to, and revolving or rotating upon theagitator or stirrer. When the reaction is carried to completion from theaforementioned thick paste state, the product contains a relativelysmall proportion of evenly shaped finely divided particles compared tothe proportion of such fines obtained when the polyolefin is charged atlow concentrations, i.e. at 5.3% by weight or less or especially at 3.5%by weight or less based on the vinyl halide employed. The product alsocontains, one or several massive irregularly shaped agglomerates whichagglomerate or agglomerates can in extreme cases comprise a major or apredominant part of the polymer product. The particulate product of thereference process normally has hard fused surfaces and generally largeparticles therein must be comminuted, e.g. by grinding or equivalentpulverization process, to make them suitable for conventional polymerprocessing steps. The latter operations generally entail handling thepolymer in a fluid melted state. Accordingly, polymer processing of theaforementioned large particles or massive agglomerates entailsundesirable, costly expenditure of mechanical energy in pulverization ofthe particles. Alternative direct melting or fusion of the productscontaining the massive agglomerates and a large proportion of relativelylarge particles also generally requires prolonged heating of the productwhich can affect deleteriously the polymer color and/or degrade thepolymer. The large product particles and agglomerates obtained byemploying the aforementioned relatively high amounts of polyolefin inthe reference process are generally less homogeneous than small productparticles since high local concentrations of monomer, polyolefin andreaction initiator build up within the large particles and especiallywithin the massive agglomerates absent effective mixing within theselarge particles during their formation in the thick paste state.Additionally, poor heat transfer from within the relative massive bodyof these particles deleteriously affects the homogeneity of the polymerwithin the particle.

The reference process generally prescribes agitation of thepolymerization mass, but as pointed out above and as illustrated inExample 2 below such agitation does not prevent formation of productagglomerates and undesirably large proportions of large particles in theproduct when the aforementioned large concentrations of polyolefin areemployed in the polymerization. Moreover increasing the speed of theagitation in the reaction would not be a feasible method of overcomingthe aforementioned disadvantages of the reference process, since in thethick paste state of the polymerization wherein the undesirableagglomerates and large particles arise, the dough-like reaction masscollects upon, and revolves with, the rotating or revolving agitator orstirrer. Accordingly, increasing the speed of the agitation would notincrease the internal mixing in the agglomerated reaction mass andmight, especially at extremely high agitation speeds, damage theagitator or the agitator motor.

SUMMARY OF THE INVENTION

According to the invention the disadvantages associated with the priorart process are overcome by an improvement in the process forpreparation of a vinyl halide polymer which comprises polymerizing inbulk a vinyl halide monomer, in liquid phase, either alone or incombination with up to about 50% by weight of another ethylenicallyunsaturated monomer copolymerizable therewith in the initial presence ofmore than about 1.8% by weight based on said vinyl halide monomer of apolyolefin or mixture of polyolefins having a weight average molecularweight of at least about 50,000. This improvement comprises removingfrom the polymerization mass during the thick paste state thereof asufficient amount of the vinyl halide in the polymerization mass toraise the effective concentration of said polyolefin to above about 3.5weight percent based on vinyl halide remaining in said mass after saidremoval of vinyl halide, whereby polymerization mass agglomerates arebroken up and a more finely divided particulate product of high impactstrength is obtained.

In general the present process permits relatively high effectiveconcentrations of the polyolefin to be employed in the prior art vinylhalide polymerization process of aforementioned U.S. application Ser.No. 674,202 to obtain finely divided polymer products of a relativelygreat concentration of grafted polyolefin, e.g. above about 6.0%,usually above about 8%, based on the weight of the product, and hence animproved impact strength, e.g. about 10 to 20 foot-pounds per inch asmeasured by the Notched Izod Impact Test. (ASTM D-256). The removal ofvinyl halide monomer in accord with the invention provides asubstantially more finely divided product than when such removal isomitted, i.e., the proportion of smaller size particles e.g. particlesof cross sectional width less than about 1.2 mm, in the product issubstantially increased, typically by about 200% or more, and themaximum product particle size is greatly diminished, typicallytwenty-fold or more, as illustrated by a comparison of the results ofExamples 1 and 2 below. Accordingly, to obtain homogeneously pulverizedpolymer suitable for conventional polymer processing, substantially lessmechanical work is required for comminution of the present polymerproducts than is required for comparable agglomerated polymers obtainedby the prior art process. Alternatively, if it is desired to process thepresent polymers without a preceding comminution step, the presentfinely divided polymers are found to require, in general, shorterheating for melting than is the case with the comparable referenceprocess products containing massive agglomerates and substantiallygreater proportions of larger particles. Thus on melting, the presentpolymer products are exposed to extreme temperatures for shorter periodsthereby diminishing the deleterious effect that such temperatures mayhave upon polymer stability and color. Since the present productcontains a substantially greater proportion of smaller size particlesand is devoid of the massive product agglomerates obtained in the priorart process when effective polyolefin concentrations above about 3.5% orespecially above about 5.3% are employed, the particulate product of theinvention is also of a more homogeneous constitution than the referenceproduct.

It was highly surprising to discover that vinyl halide monomer removalin accordance with the invention was effective in breaking up reactionmixture agglomerates since, in general, the prior art associated withvinyl halide bulk polymerization has taught such removal to beundesirable or has prescribed addition of vinyl halide to thepolymerization mass to break up agglomerates. Thus U.S. Pat. No.2,230,240 to H. L. Gerhart which is directed to bulk polymerization of avinyl compound, e.g. vinyl halide, and a maleic anhydride comonomerrequires the reaction to be carried out under a sufficient reactionpressure to prevent escape of the vinyl monomer since such removal byventing causes ebullition of the polymerization mass which impairs thehomogeniety of the product. Moreover, U.S. Pat. No. 2,961,432 to H.Fikenscher et al. which contemplates bulk polymerization of a vinylcompound, e.g. vinyl halide, in the presence of a polymer thereofteaches (see Col. 3, lines 15-21) that is especially desirable to addvinyl monomer in vapor form to the agitated polymerization mass to avoidagglomeration in the reaction mixture, which teaching contradicts theimprovement step of the present invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF

Except for the above-defined improvements of the invention, thereactants and reaction conditions, e.g. reaction temperature andpressure, are substantially the same as those of the polymerizationdisclosed in the aforementioned U.S. applications, Ser. Nos. 746,046 and674,202, the disclosures of which are incorporated herein by reference.

The vinyl halide utilized in the present process is preferably vinylchloride, although other vinyl halides such as vinyl fluoride and vinylbromide can be employed also.

In carrying out the present improved process the vinyl halide monomercan be removed from the thick paste state of the agitated polymerizationreaction mass in any suitable way. For example, the liquid monomer maybe filtered from the bulk reaction mass e.g. by passage through apressure filter. The filtrate is then distilled outside the reactionvessel with the distillation residue containing initiator and unreactedpolyolefin being returned to the reaction vessel. However, since thepolymerization is generally carried out under at least autogeneoussuperatmospheric pressure, especially when vinyl chloride is employed asthe vinyl halide reactant, removal of the vinyl halide is preferablyachieved by venting the reaction mixture to a pressure zone e.g. theatmosphere, wherein the pressure is substantially below the reactionpressure. Removal by venting is especially desirable since it promotesrapid removal of heat from the reaction mass. Vinyl halide monomerremoval is commenced during the above-described thick paste state of thereaction the duration of which corresponds to conversion to polymer ofabout 25% to about 45%, more typically about 30% to about 40% by weightof vinyl halide, based on vinyl halide charged. The onset of the thickpaste state is generally accompanied by a rapid increase in the heatevolved from the reaction, i.e. by a rapid increase in the reactionisotherm as evidenced by a sharp increase in reaction pressure.Preferably vinyl halide removal in accordance with the invention iscommenced about 5 minutes to about 15 minutes after beginning of thethick paste state of the polymerization. The venting of vinyl halidefrom the reaction mass according to the preferred mode of removal ofvinyl halide may be carried out in continuous fashion, or alternativelyand desirably, in intermittent but regular fashion with the reactionmass being restored, after each release of vinyl halide, substantiallyto the temperature and pressure prevailing in the reaction mass prior toeach release of the monomer. The polymerization vessel is desirablyequipped with a conventional adjustable valve to facilitate venting.

The amount of vinyl halide monomer which is removed during the thickpaste state of the polymerization reaction in order to avoid productagglomerates according to the invention is generally a minor proportionof the vinyl halide employed in the polymerization, i.e. less than about50 weight percent of the vinyl halide charged. Preferably, however, toretain substantially all of the benefits and advantages of the prior artpolymerization process of aforementioned applications U.S. Ser. Nos.746,046 and 674,202, no more than about 40 weight percent, typically nomore than about 30 weight percent of the vinyl halide charged to thepolymerization is removed in the present process. While some improvementin obtaining finely divided polymer product of small maximum particlesize can be achieved by removing only small amounts, say 2 to 3% byweight, of vinyl halide during the thick paste state of thepolymerization, it is preferred to remove at least about 5 weightpercent of the vinyl halide charged in the practice of the invention.Preferably, the percentage of vinyl halide removed can vary from about 8to 15% up to about 25 to 35%, and is more preferably about 15 to 35%based on the vinyl halide charged.

The rate of removal of vinyl halide by venting or other removaltechnique can be varied over a wide range but usually is about 0.1% toabout 1.5% preferably about 0.15% to about 1.2% per minute based on theweight of vinyl halide charged. An especially good result is generallyobtained when the vinyl halide is removed from the polymerization massat a rate which can range from about 0.3% to about 0.8% up to about 1.0%or even up to about 1.2% by weight per minute.

The proportion of vinyl halide and polyolefin charged initially to thepolymerization may vary over a wide range but should be sufficient toprovide, after vinyl halide removal in the thick paste state, aneffective polyolefin concentration of from above about 3.5% to about 20%by weight, preferably at least above about 5.3% and especially is about5.5% to about 10% by weight computed on the amount of vinyl halideremaining after removal of vinyl halide according to the invention, i.e.on the amount of vinyl halide charged minus the amount of vinyl halideremoved in the thick paste state of the polymerization. An especiallygood result is generally obtained when the initial charge of polyolefinand vinyl halide and the amount of vinyl halide removed in the thickpaste state of the reaction are sufficient to provide an effectivepolyolefin concentration of about 6 to about 8% or even up to about 9%by weight. Usually the initial concentration of polyolefin and vinylhalide in the polymerization are such as to provide a reaction mixturecontaining before venting or other removal of the vinyl halide, aboveabout 1.8% and desirably at least about 3%, typically about 3.5% orgreater of polyolefin based on the weight of vinyl halide charged.

While the exact chemical nature of the polymer formed by the process ofthe present invention is not known, it is believed that a graftcopolymer is formed in which the vinyl halide polymer forms upon thepolyolefin polymer. To obtain a maximum reduction in melt viscositywhich is a standard measure of processability, the polymer used as thetrunk polymer in graft polymerization should be incompatible with thevinyl halide polymer formed. During the processing of a polymer of avinyl halide such as in molding, the physical properties of the polymerchange during the processing as the result of the polymer being held athigh temperatures for long periods of combination with the internal heatbuilt up as a result of shear forces produced by the processingmachinery. Thus, the physical properties of a graft polymer having atrunk polymer which is compatible with the vinyl halide polymer canchange during processing as the result of solubilization of the trunkpolymer into the polyvinyl halide. In such a case, the impact strengthwould decrease during the processing. Therefore, the compositions of thepresent invention are directed to graft copolymers having a polyolefinbackbone polymer which is incompatible with the vinyl halide polymerformed thereon. With such an incompatible polymer backbone, the physicalproperties of the graft copolymer do not change during processing, sincethe incompatibility prevents the solubilization of the trunk polymer inthe polyvinyl halide. The melt viscosity is reduced by the choice of agraft copolymer and is not affected by the usual subsequent processingconditions.

The melt viscosity of the graft copolymer formed also depends upon themolecular weight of the trunk polymer, as well as the vinyl halidepolymer formed thereon. A maximum reduction of melt viscosity can beexpected from the graft copolymer where the trunk polymer is chosen soas to have low molecular weight, e.g. a weight average molecular weightof 50,000 to 150,000 and the vinyl halide monomer is polymerized so asto have a reasonably low molecular weight also, such low molecularweight olefin polymers being preferred for especially easy processing inthe molten state. Preferably to produce polymer products of excellentimpact strength, i.e. of high graft polyolefin content or high graftingefficiency, the weight average molecular weight of the polyolefin mayrange from about 150,000 to about 1,000,000 or higher and is especiallyabout 150,000 to about 400,000.

While vinyl chloride is the preferred vinyl halide reactant of theinvention, other suitable vinyl halide monomers useful in the inventionare the alpha-halo-substituted ethylenically unsaturated compounds whichlike vinyl chloride are capable of entering into an additionpolymerization reaction, for example, vinyl fluoride, vinyl bromide,vinyl iodide, vinylidene fluoride, vinylidene chloride, vinylidenebromide, vinylidene iodide and the like. The polymers of the presentinvention can be formed of the same or different alpha-halo-substitutedethylenically unsaturated materials and, thus, the invention includeshomopolymers, copolymers, terpolymers, and interpolymers formed byaddition polymerization. Illustrative of these copolymers is a copolymerof vinyl chloride and vinylidene chloride.

While it is preferred that the monomer composition be comprised totallyof vinyl halide monomer, e.g. vinyl chloride alone, the presentinvention is also intended to include copolymers formed by thefree-radical addition polymerization of a monomer composition containinga predominant amount, e.g., at least 50 percent of vinyl halide and aminor amount, e.g., less than 50 percent by weight of anotherethylenically unsaturated monomer composition copolymerizable therewith.Preferably, the other ethylenically unsaturated monomer is used inamounts of 20 percent or less by weight and more preferably in amountsof 10 percent or less by weight of the total monomer used in preparingthe polymer. Suitable ethylenically unsaturated compounds which can beused to form copolymers, terpolymers, tetrapolymers, interpolymers andthe like, are illustrated by the following monoolefinic hydrocarbons,i.e., monomers containing only carbon and hydrogen, including suchmaterials as ethylene, propylene, 3-methylbutene-1, 4-methylpentene-1,pentene-1, 3,3-dimethylbutene-1, 4,4-dimethylbutene-1, octene-1,decene-1, styrene and its nuclear alpha-alkyl or aryl substitutedderivatives, e.g., o-, m- or p-methyl, ethyl, propyl or butyl styrene;alphamethyl, ethyl, propyl or butyl styrene; phenyl styrene, andhalogenated styrenes such as alpha-chlorostyrene; monoolefinicallyunsaturated esters including vinyl esters, e.g., vinyl acetate, vinylpropionate, vinyl butyrate, vinyl stearate, vinyl benzoate,vinyl-p-chlorobenzoates, alkyl methacrylates, e.g., methyl, ethyl,propyl and butyl methacrylate; octyl methacrylate, alkyl crotonates,e.g., octyl; alkyl acrylates, e.g., methyl, ethyl, propyl, butyl,2-ethyl hexyl, stearyl, hydroxyether and tertiary butylamino acrylates,isopropenyl esters, e.g., isopropenyl acetate, isopropenyl propionate,isopropenyl butyrate and isopropenyl isobutyrates; isopropenyl halides,e.g., isopropenyl chloride; vinyl esters of halogenated acids, e.g.,vinyl alpha-chloroacetate, vinyl alpha-chloropropionate and vinylalpha-bromopropionate; allyl and methallyl esters, e.g., allyl chloride,allyl cyanide; allyl chlorocarbonate, allyl nitrate, allyl formate andallyl acetate and the corresponding methallyl compounds; esters ofalkenyl alcohols, e.g., beta-ethyl allyl alcohol and beta-propyl allylalcohol; halo-alkyl acrylates, e.g., methyl alpha-chloroacrylate andethyl alpha-chloroacrylate, methyl alpha-bromoacrylate, ethylalpha-bromoacrylate, methyl alpha-fluoroacrylate, ethylalpha-fluoroacrylate, methyl alpha-iodoacrylate and ethylalpha-iodoacrylate; alkyl alpha-cyanoacrylates, e.g., methylalpha-cyanoacrylate and ethyl alpha-cyanoacrylate; maleates, e.g.,monomethyl maleate, monoethyl maleate, dimethyl maleate, diethylmaleate; and fumarates e.g., monomethyl fumarate, monoethyl fumarate,dimethyl fumarate, diethyl fumarate; and diethyl glutaconate;monoolefinically unsaturated organic nitriles including for example,fumaronitrile, acrylonitrile, methacrylonitrile, ethacrylonitrile,1,1-dicyanopropene-1, 3-octenenitrile, crotonitrile and oleonitrile;monoolefinically unsaturated carboxylic acids including for example,acrylic acid, methacrylic acid, crotonic acid, 3-butenoic acid, cinnamicacid, maleic, famaric and itaconic acids, maleic anhydride and the like.Amides of these acids, such as acrylamide, are also useful. Vinyl alkylethers and vinyl ethers, e.g., vinyl methyl ether, vinyl ethyl ether,vinyl propyl ether, vinyl n-butyl ether, vinyl isobutyl ether, vinyl2-ethylhexyl ether, vinyl 2-chloroethyl ether, vinyl propyl ether, vinyln-butyl ether, vinyl isobutyl ether, vinyl 2-ethylhexyl ether, vinyl2-chloroethyl ether, vinyl cetyl ether and the like; and vinyl sulfides,e.g., vinyl beta-chloroethyl sulfide, vinyl beta-ethoxyethyl sulfide andthe like can also be included. Diolefinically unsaturated hydrocarbonscontaining two olefinic groups in conjugated relation and the halogenderivatives thereof, e.g., butadiene-1,3; 2-methyl-butadiene-1,3;2,3-dimethylbutadiene-1,3; 2-chloro-butadiene-1,3;2,3-dichloro-butadiene-1,3; 2-bromo-butadiene-1,3; and the like can alsobe used.

Specific monomer compositions for forming copolymers can be illustratedby vinyl chloride and/or vinylidene chloride and vinyl acetate, vinylchloride and/or vinylidene chloride and maleic or fumaric acid esters,vinyl chloride and/or vinylidene chloride and acrylate or methacrylateester, vinyl chloride and/or vinylidene chloride and vinyl alkyl ether.These are given as illustrative of the numerous combinations of monomerspossible for the formation of copolymers. The present invention includesall such combinations.

The free radical bulk polymerization of the monomer composition isconducted in the presence of an olefin homopolymer, copolymer,terpolymer, or tetrapolymer and halogenated derivatives thereof. Theolefin polymers can also contain a diene as a monomer unit.

Suitable monomers are propene, butene-1, isobutene, pentene, hexene,heptene, octene, 2-methylpropene-1, 3-methylbutene-1, 4-methylpentene-1,4-methylhexene-1, 5-methylhexene-1.

Suitable comonomers are those utilized to prepare homopolymers as listedabove such as propene or butene-1 with ethene or isobutylene withisoprene, ethene with vinyl acetate, ethene with ethyl acrylate, and thelike. Suitable termonomers are those utilized to prepare homopolymersand copolymers as disclosed above such as propene, ethene and the likecontaining up to 15 percent preferably up to about 6 percent by weightof a diene such as dicyclopentadiene, butadiene, cyclooctadiene andother non-conjugated dienes with linear or cyclic chains.

The polyolefins used are characterized by being soluble, partiallysoluble or dispersible at normal room temperature and pressure in vinylchloride monomer and if a homopolymer having monomeric units with 2 to 8carbon atoms; if copolymers, having monomeric units with 2 to 8 carbonatoms; and if a halogenated polymer, having monomeric units with 2 to 8carbon atoms. Suitable halogenated polyolefins are the chlorinated,brominated, or fluorinated polyolefins. The weight average molecularweight of the olefin polymers, copolymers, terpolymers, andtetrapolymers can vary from about 50,000 to about 1,000,000 and higheras described above.

The free radical bulk polymerization can take place in accordance withthe process of the invention at temperatures between about 25° and about90°, preferably about 40° to about 80°, and especially about 50° toabout 75°, centigrade. The polymerization reaction is conducted in thepresence of a small initiating amount of a free radical initiator forthe reaction. Useful free-radical initiators are organic or inorganicperoxides, persulfates, oxonides, hydroperoxides, peracids andpercarbonates, diazonium salts, diazotates, peroxysulfonates, trialkylborane-oxygen systems, amine oxides, and azo compounds such as2,2'-azo-bis-isobutyronitrile and 2,2'-azo-bis-2,4-dimethylvaleronitrile. Preferably an azo compound or an organic peroxy compound,especially an organic peroxide, is used as the initiator. The initiatoris used in a concentration ranging from about 0.01 to about 1.0% andpreferably about 0.05 to about 0.5% based on the total weight of allmonomers in the reaction mixture. Organic initiators which haveparticularly good solubility in the bulk polymerization mass asdisclosed aforementioned U.S. application Ser. No. 674,202, and hence,are especially useful in the practice of the inventors including thefollowing representative examples: lauroyl peroxide, benzoyl peroxide,diacetyl peroxide, azobisisobutyronitrile, diisopropylperoxydicarbonate, azo-bisisobutyramidine hydrochloride, t-butylperoxypivalate, 2,4-dichloro-benzoyl peroxide, and2,2'-azo-bis-(2,4-dimethyl valeronitrile). These and other suitableinitiators are more particularly described by J. Brandrup and E. H.Immergut, Editors "Polymer Handbook", Interscience Publishers, 1966,Chapter II entitled "Decomposition of Organic Free Radical Initiators",the pertinent disclosure whereof is incorporated herein by reference.Advantageously, the initiator which is used is chosen from a group ofinitiators known in the prior art as the "hot catalysts" or those whichhave a high degree of free-radical initiating activity. Initiators witha lower degree of activity are less desirable in that they requirelonger polymerization times. Also, long polymerization times may causepreliminary product degradation evidenced by color problems, e.g.,pinking.

The present process is preferably carried out in a single stage bulkoperation but, if convenient or desired, the reaction can be effected ina two stage reaction configuration in which high speed, high shearagitation is used during a first stage, and low speed, low shearagitation is used in a second stage. Two stage bulk polymerizationprocesses for vinyl halide and vinyl halide-comonomer mixtures which areuseful in the practice of the invention are described in aforementionedU.S. applications Ser. Nos. 746,046 and 674,202, as well as British Pat.No. 1,047,489 and U.S. Pat. No. 3,522,227, to Thomas the pertinentdisclosure of which patents is incorporated herein by reference.

In the following abbreviated description of a typical two stage reactionconfiguration for carrying out the present process, for the sake ofsimplicity, the initial stage of the polymerization or copolymerizationwill be referred to as first stage reaction and the vessel in which thisinitial stage of polymerization is carried out will be referred to as"Prepolymerizer". The final or complementary stage of the polymerizationwill be called simply second stage reaction and the vessel in which itis carried out the "Polymerizer".

In the first stage reactor, the means chosen to agitate the monomer ormonomers is of a type capable of providing high shear agitation and iscommonly referred to as a "radical turbine type" agitator. At the startof the first stage reaction, the Prepolymerizer is charged with amonomer composition to which an initiator has been added. Anypolymerization generally used in bulk polymerization methods, that is,those hereinabove described, can be used to an extent which is usual forbulk polymerization processes. After addition of the vinyl chloridemonomer to the first stage reactor, a small amount of monomer is ventedin the process of removing the air from the first stage reactor vessel.The speed of the turbine type agitator generally lies between 500 and2,000 revolutions per minute or a tip speed of about 2 to 7 meters persecond in the first stage reactor. A tip speed of at least about 0.1,and preferably, about 0.5 to about 2 meters per second is used in thesecond stage reactor. These figures should not be regarded as limitingvalues. As soon as a conversion of at least about 3 to about 20 percentof the monomer composition has been obtained in the first stage reactor,the contents of the vessel are transferred to a second stage polymerizervessel equipped to provide slow speed, low shear agitation so as toinsure proper temperature control of the reaction medium. Preferably theconversion in the first stage reactor is about 3 to about 15 percent andis especially about 7 to about 15 percent. The reaction temperature inboth first and second stage reactors generally ranges between about 25degrees centigrade to about 90 degrees centigrade, preferably about 40°to about 80 degrees centigrade. The reaction pressure in the first stagereactor is also at least an autogeneous superatmospheric pressuregenerally in the range between about 80 to about 210 pounds per squareinch, and preferably between about 90 to about 190 pounds per squareinch.

Since the minimum conversion (e.g. about 25-30%) of vinyl halidecorresponding to onset of the thick paste state of the polymerizationinvariably occurs in the second reaction stage of the above describedtwo stage reaction configuration, vinyl halide monomer is always removedfrom the second stage of the two stage reaction process in accordancewith the invention. Moreover, as will be evident to those skilled in theart, the conditions of temperature pressure and agitation of the secondstage are substantially similar to, and hence, typify those used whencarrying out the present improved polymerization in a single reactionstage.

The improved polymerization product of the invention is recovered fromthe polymerization reaction vessel in conventional fashion, e.g., byexpelling unreacted monomers by venting. The present finely dividedproducts are easily ground or otherwise comminuted to a homogeneouspowder for admixture with conventional inert additives such as fillers,dyes, and pigments. In addition, the polymerization products can beadmixed with plasticizers, lubricants, thermostabilizers and ultravioletand light stabilizers as desired. If desired the present product can bedirectly melted for combination with the aforementioned additives andsubsequent molten processing, such as molding and extrusion. The meltingor fusion of the present polymers which contain predominantly, finelydivided particles, occurs so rapidly as to avoid any seriousdecomposition or color-degradation caused by exposure to elevatedtemperature during the melting or fusion operation.

The exact mechanism by which the present process effectively breaks upreaction mixture agglomerates is not understood completely, but whilethe invention is not bound to any theory it is surmised that removal ofvinyl halide in accord with the invention increases the ratio of solidphase, i.e. polymer, to liquid phase, i.e. vinyl halide monomercontaining dissolved or dispersed polyolefin, in the reaction mass andhence rapidly advances the reaction mass out of the thick paste stateinto the fluid powder state described hereinabove.

In order to further illustrate the invention but without being limitedthereto, the following examples are given. In this specification andclaims, unless otherwise indicated, parts, percentages and proportionsare by weight and temperatures are in degrees centigrade.

EXAMPLE 1

A two liter cylindrical glass reaction vessel is equipped with a beakerbar agitator operating at about 200 revolutions per minute at a tipspeed of about 0.1 meters per second, a pressure sensor, and a ventingvalve and is surrounded by a jacket containing aqueous constanttemperature heating bath. The reactor is charged with 45.0 g. of apolyolefin mixture of average weight average molecular weight of 330,000which is a 3:4 mixture of 19.3 g. of Epsyn 7006 (an ethylene propylenecopolymer of weight average molecular weight of 225,000 manufactured byCopolymer Corp.) and 25.7 g. of SK43A (an ethylene propylene copolymerof weight average molecular weight of 420,000 manufactured by CopolymerCorp.) and 0.7 g. of lauroyl peroxide initiator. The reaction vessel ischecked for leaks by pressurization with nitrogen, evacuated to asubatmospheric pressure of about 5 mm, and charged with 745 g, of vinylchloride. After the vessel is sealed, about 80 g. of the vinyl chlorideis vented from the reaction vessel to remove entrapped air therebyproviding a net charge of vinyl chloride of about 665 g. and an initialpolyolefin concentration of about 6.77% based on the weight of the vinylchloride. The reaction mass is heated with agitation to a temperature ofabout 70°-72° under an autogeneous pressure of about 170-175 p.s.i.g. toinitiate the polymerization. The polymerization mass changes from asubstantially clear solution or dispersion, to an opaque slurry. Afterabout 1.5 hours, there is a sharp increase in the reaction exotherm,i.e. in the heat evolved from the reaction mass as evidenced by a risein reaction pressure. At about the same time, the consistency of thereaction mixture becomes similar to that of dough indicating the onsetof the thick paste state of the polymerization. After about 5 minutesfrom the exotherm increase, the venting valve of the reactor is openedintermittently but regularly over a period of 30 minutes to vent about8% of the vinyl chloride (based on net vinyl chloride changed) to anexhaust at atmospheric pressure at an average rate of about 0.267percent per minute so that the effective concentration of polyolefin isabout 7.37% (based on net vinyl chloride charged less vinyl chloridevented). On completion of the venting operation the polymerizationrapidly advances to the powder state of polymerization, i.e. thepolymerization mass changes from a highly viscous dough-like paste tosubstantially fine, nonviscous powder. The reaction is allowed toproceed under the foregoing conditions of temperature, pressure andagitation until no more liquid monomer is observed in the reactionvessel and the pressure therein begins to drop indicating the end of thepolymerization. The duration of the polymerization from inception ofinitiation is about 2.9 hours.

The polymerization vessel is vented to the atmosphere to remove residualvinyl chloride. The particulate polymer in the reaction vessel (313 g.)together with scrapings from the reactor bottom and walls and theagitator, i.e. bottom cake, wall scale and stirrer deposit (61 g. about16.3% of total product) amount to a product yield of 374 g. of whichabout 12.3% is polyolefin in both grafted and free dispersed form sothat the amount of polymer obtained from vinyl chloride is 329 g.corresponding to a conversion of about 50% based on net vinyl chloridecharged to the reaction.

The particulate portion of the product is then passed through a No. 16mesh sieve (U.S. standard sieve size). The amount of particulate polymerfines, i.e. particles of average cross-sectional width of about 1.2 mmor less, which passes through the sieve is 108 g. (about 29% of totalpolymer product). The amount of particulate polymer retained on thesieve, i.e. polymer particles of average cross-sectional width greaterthan about 1.2 mm, is 205 g. (55%) of which about 114 g. issubstantially evenly shaped granular polymer of average cross-sectionalwidth of about 1.2 mm to about 10 mm, about 49 g. is globular polymer ofaverage cross sectional width of about 10 to about 25 mm and about 42 g.is in the form of three irregular agglomerates or lumps having anaverage cross sectional width (measured across their widest dimension)of about 30 mm.

The above mentioned particulate fraction of the product is tested forimpact strength by the Notched Izod Impact Test, according to theprocedure of ASTM-D256. Samples for use in this test are prepared bymixing together 100 parts of the polymer, 5 parts of Acryloid K120-ND(an acrylic polymer processing aid manufactured by Rohm and Haas Co.)and 2 parts Thermolite 31 [di-n-butylin S,S'-bis(isooctylmercaptoacetate) thermal stabilizer, manufactured by M and T ChemicalsInc.]. The mixture is milled on a two roll Farrell mill for 5 minutes atabout 188° and compression molded into a sheet of 1/8 inch thickness ona Carver press. The sheet is cut into uniform 0.5 inch by 2.5 inch teststrips.

The Izod Impact (notched) strength is excellent, being in the range ofabout 10 to 18 foot-lbs, per inch.

The percent grafting in the polymer product is determined by extractingthe free ungrafted polyolefin and vinyl chloride homopolymer andrecovering vinyl chloride-polyolefin graft polymer from the polymerproduct employing a procedure similar to that described in Example 3 ofaforementioned U.S. application Ser. No. 674,202. The vinylchloride-polyolefin graft polymer is analyzed for percent chlorine by aconventional analytical technique. The percentage of chlorine obtainedis divided by 56.8%, the percent chlorine in conventional vinyl chloridehomopolymer, to determine the percentage of vinyl chloride in the graftpolymer. The latter percentage on subtracting from 100 gives the percentgrafted polyolefin in the graft polymer. From the latter percentage andthe percentage of free ungrafted polyolefin in the product the percentgrafting in the total polymer is computed. The present polymer productis characterized by a percent grafting of 84% (corresponding to a vinylhalide-polyolefin graft polymer content in the product of about 10.3%).

EXAMPLES 2-6

The procedure of Example 1 is repeated substantially as described inExamples 3-5 employing net changes of vinyl chloride of about 660 to 670g. of vinyl chloride and several process variations as noted in theTable below which summarizes the results of these experiments incomparision with those of Example 1. Examples 2 and 6, the results ofwhich are also summarized in the Table are control experiments which arecarried out employing substantially the same process conditions as thoseof Examples 1,3-5 except that no vinyl chloride is removed during thepaste state of the polymerization.

By comparision of the results of Examples 1, 3-5 with those of controlExample 2 it is apparent that removal of vinyl chloride monomer duringthe thick paste state in accordance with invention provides a vinylchloride-polyolefin polymer of high impact strength with improved smallparticle size, i.e. a greater proportion of the product is particulatepolymer having an average cross sectional width of less than about 1.2mm while the average cross sectional width of the largest polymerparticle is reduced from about 700 mm (as in control Example 2) to about30 mm (as in Example 1).

From comparison of the results of control Example 6 with those ofExamples 1-5 it is also apparent that a satisfactory excellent impactstrength as measured by the highly discriminating Notched Izod ImpactStrength Test is obtained when the percentage of grafted polyolefin inthe polymer product is greater than about 6 percent.

Control Example 6 illustrates that whereas an initial concentration of5.3% polyolefin in the polymerization reaction mass provides a polymerproduct of desirably small particle size such a small concentration ofpolyolefin in the reaction mixture, when it remains the effectivepolyolefin reaction concentration by omission of the monomer removalstep of the invention, produces polymer product of low graft polyolefincontent, i.e. 6% or less, and, hence, of unsatisfactory, inferior impactstrength compared to that of the products of corresponding Examples 3-5.In the latter examples, the polymerization masses have initialpolyolefin concentrations of about 5.3% as in Example 6 but monomerremoval in accord with the invention in these examples raises theeffective polyolefin reaction concentration to about 6.9% to about 7.6%resulting in products of enhanced impact strength.

                                      TABLE I                                     __________________________________________________________________________         Net                                                                           Vinyl               Effective     Time of Beginning                                                                             % Conversion                Chloride                                                                           % Vinyl Chloride                                                                       %     % Con- Rate   of Venting After                                                                        Duration                                                                            of Vinyl Chlo-              Charged                                                                            Vented During                                                                          Polyolefin                                                                          centration of                                                                        of Venting                                                                           Inception of Thick                                                                      Venting                                                                             ride (Duration         Example                                                                            (g.) Thick Paste State                                                                      Charged                                                                             Polyolefin                                                                           (% per min.)                                                                         Paste State (min.)                                                                      (min.)                                                                              of                     __________________________________________________________________________                                                           Reaction)              1    665   8       6.77  7.37   0.267   5        30    50 (2.9 hrs.)          2    665  none     6.77  6.77   0      --        0     58 (4.3 hrs.)          (Control)                                                                     3    660  30       5.3   7.57   1.2     5        25    41 (2.3 hrs.)          4    665  24       5.27  6.92   0.8    10        30    47 (2.5 hrs.)          5    670  27       5.23  7.15   0.9    20        30    44 (2.3 hrs.)          6    660  none     5.3   5.3    0      --        0     71 (3.5 hrs.)          (Control)                                                                     __________________________________________________________________________                                      Particulate Product                                                  % Total Product                                                                        % Total Product                                  % Total             ≦about 1.2 mm                                                                   >About 1.2 mm                                                                           Largest Particle                       Polyolefin                                                                           % Grafting (% Graft                                                                        Cross Sectional                                                                        Cross Sectional                                                                         Size in Particulate                                                                    % Non-Particulate        Example                                                                            in Product                                                                           Polyolefin in Product)                                                                     Width    Width     Product (mm)                                                                           Product                  __________________________________________________________________________    1    12.3   84 (10.3)    29       55        30       16                       2    10.4   83 (8.7)     11       82        700      7                        (Control)                                                                     3    11.5   --           36       48        --       14                       4    10.0   85 (8.5)     57       27         5       16                       5    10.5   79 (8.8)     54       30        15       16                       6    7.0    86 (6.0)     60       22        15       16                       (Control)                                                                     __________________________________________________________________________     NOTE:                                                                         The particulate products of Examples 1-3,5 have excellent Notched Izod        Impact strengths in the range of about 10-13 ft. lbs. per inch. The           particulate product of Example 4 has an exceptionally fine impact strengt     of 19 ft. lbs. per inch, while the impact strength of the particulate         product of control Example 6 is poor being only about 2 ft. lbs. per inch                                                                              

EXAMPLE 7

The procedure of Example 1 is repeated substantially as described exceptthat the net charge of vinyl chloride is 670 g., the polyolefin is 42.5g. of a mixture (average weight average molecular weight, 390,000) of 10g. of Epsyn 7006 and 32.5 g. of SK 43A corresponding to an initialpolyolefin concentration of 6.34% based on net vinyl chloride charged,vinyl chloride removal by venting is commenced about 10 minutes afterthe increase in the reaction exotherm which indicates the beginning ofthe thick paste state of the polymerization, venting of vinyl chlorideis continued for 15 minutes to remove about 10% of the vinyl chloridecharged (providing an effective polyolefin concentration of about 7.05%)at an average rate of about 0.33% per minute and the duration ofreaction is 2.8 hours. The particulate polymer in the reaction vessel(321 g.) together with cake from the reactor bottom (41 g.), reactorwall scale (16 g.) and deposit on the agitator (50 g.) amounts to aproduct yield of 371 g. of which about 11.5% is polyolefin in graftedand free dispensed form so that the conversion of vinyl chloride topolymer is 328 g. (52%). On screening the particulate portion (321 g.,71% of the total product), 98 g. (26%) is of average particlecross-sectional width less than about 1.2 mm; 166 g. (45%) is of averagecross-sectional width greater than about 1.2 mm of which 89 g. issubstantially evenly shaped granular polymer of average cross-sectionalwidth of about 1.2 mm and 77 g. is globular agglomerates of averagecross-sectional width greater than about 5 mm; the maximumcross-sectional width of such agglomerates being about 15 mm. Theparticles of width of less than about 1.2 mm and those of width betweenabout 1.2 and about 5 mm have a 10% total polyolefin content with thepercentage grafting being about 90% (corresponding to about 9% graftpolyolefin in the product) and a Notched Izod Impact strength of about16 ft.-lbs. per inch.

EXAMPLE 8

To a vertical type first stage reactor of 2.5 gallon capacity andstainless steel construction, equipped with a radial turbine-typeagitation, a pressure sensor and a venting valve, there is added 6.81kg, vinyl chloride monomer, 1.26 g. of dicyclohexyl peroxydicarbonatepolymerization initiator sold under the tradename "Lupersol 229" and0.75 g. of a 50% methanol solution of "Gelva" (a densifying agent whichis a 2:1 copolymer of vinyl acetate and crotonic acid manufactured byMonsanto Co.). About 0.908 kg. of vinyl chloride monomer are vented fromthe reactor in order to remove entrapped air. The reaction mass isheated to about 70° under an autogeneous reaction pressure of about 167psig. with the agitator operating at about 1500 rpm and agitated atthese conditions of temperature and pressure for about 25 minutes afterwhich period the conversion of vinyl chloride to vinyl chloride polymeris about 8% and the reaction mixture is ready for transfer to the secondstage reactor as described hereinbelow.

Meanwhile into the second stage reactor, which is a 5 gallon stainlesssteel vessel equipped with a spiral agitator operating at a speed ofabout 63 rpm, a pressure sensor and a venting valve, there is charged at0°, 408.63 g. of Epsyn 40A (an ethylene propylene-modified terpolymer ofabout 160,000 weight average molecular weight, wherein theethylene-propylene ratio is about 55/45 and the diene is ethylidenenorbornene present in an amount of 3±0.5 percent, manufactured by theCopolymer Corp.) which has been finely shredded and dusted with 58.38 g.of pulverulent bulk polymerized vinyl chloride polymer (to preventagglomeration and promote dissolution of the polyolefin in the reactionmixture) and 0.4 g. of 2,6-di-t-butyl paracresol antioxidant colorstabilizer. The mixture is freed of air by drawing a vacuum of about 29inches of mercury in the reaction vessel and thereafter flooding thevessel with nitrogen. After repetition of the air removal treatment,3.75 g. of the "Lupersol 229" initiator and about 7.72 kg. of additionalvinyl chloride monomer are charged to the reactor thereby providing aproportion of polyolefin based on monomer of about 3%. After thereaction vessel is sealed, the reaction mixture is heated underagitation to about 40° and the first stage reaction mixture describedhereinabove is added. The reaction mass is then maintained at thereaction temperature of about 58° under an autogeneous reaction pressureof about 130 psig. for about two hours to reach the thick paste stage ofthe polymerization reaction. About 4.54 kg. of vinyl chloride monomerare then vented from the agitated reaction mixture over a period ofabout 40 minutes to provide an effective polyolefin concentration of4.5%, with the pressure and temperature of the reaction vessel droppingto about 90 psig. and about 47°, respectively, during the ventingoperation. On completion of the venting operation, the agitated reactionmixture is heated over a period of 35 minutes to a temperature of about58° and a pressure of about 130 psig. and is maintained at the latterconditions of temperature and pressure for about 40 minutes. At the endof the latter time period a drop in the pressure in the reaction vesselindicates that the polymerization reaction is substantially complete.The reaction vessel is heated to about 70° and any unreacted vinylchloride monomer in the vessel is vented therefrom over a 45 minuteperiod. To insure as complete as possible removal of vinyl chloridemonomer residue from the product, the product is degassed in vacuo at85° for about 4 hours and subsequently at about 0° for about one hourand then is discharged from the reactor.

A pulverulent polymer product of excellent impact strength is obtainedin a yield of about 7.36 kg. (corresponding to a conversion of monomerto polymer of about 77% based on monomer charged to the polymerizationwhich does not include the monomer vented during the thick paste statein the second reaction stage). About 90.1% portion of the product passesthrough a 10 mesh screen (U.S. Standard Sieve Series). The latterportion of the product contains only about 47 parts per million ofresidual vinyl chloride monomer.

EXAMPLE 9 (CONTROL) p The procedure of Example 8 is repeatedsubstantially as described except that the amount of vinyl halidemonomer and initiator charged at the beginning of the second reactionstage is 3.18 kg. and 5.0 g. respectively, and the monomer removal stepof the invention is omitted so that the proportion of polyolefin basedon monomer in the second stage is substantially the same as that inExample 8 above subsequent to the monomer removal step, i.e. about 4.5%.The product which has satisfactory impact resistance is obtained in ayield of 7.72 kg. (corresponding to a conversion of monomer to polymerof about 80% based on monomer charged to the polymerization). Only about60% of the product is capable of passing through the 10 mesh screendescribed in Example 8. The amount of residual vinyl chloride monomer inthe product fraction which passed through the 10 mesh screen is about900 ppm. Comparision of the results of this example with that of Example8 above illustrates that the process of the invention effects asubstantial enhancement of the proportion of small size productparticles obtained and a substantial diminution of residual vinylchloride monomer therein even when, as shown in Example 8, the effectiveconcentration of the polyolefin subsequent to the monomer removal stepis substantially below the preferred value of about about 5.3%.

The following Example 10 together with the following Control Example 11illustrate that the invention is effective in providing the beneficialprocess improvements, as described hereinabove, as well as providing adistinctive improved reaction product, according to the invention, whenthe polyolefin reactant employed has a weight average molecular weightin the range of about 50,000 to about 150,000.

EXAMPLE 10

To an agitator-equipped reactor substantially similar to that employedin Example 1 there is charged, following the procedure of Example 1, amixture of 770 g. of vinyl chloride monomer, 0.7 g. of lauroyl peroxideinitiator and 60 g. of an ethylene-propylene copolymer of a weightaverage molecular weight of about 80,000 (manufactured under thedesignation SP908-5 by the Copolymer Corp.). The reactor is sealed andabout 50 g. of the vinyl chloride monomer is vented from the reactorsubstantially as described in Example 1 to remove entrapped air so thatthe net charge of vinyl chloride monomer to the reaction is about 720 g.(corresponding to an initial olefin trunk polymer reactant concentrationof about 8.3% based on the net charge of vinyl chloride monomer). Thereaction mass, which is agitated substantially as described in Example1, is heated to about the reaction temperature and autogeneous reactionpressure as described in Example 1 to initiate the polymerization. Afterabout 3.4 hours from the establishment of the foregoing reactionconditions of temperature and pressure, the onset of the thick pastestate of the polymerization reaction mass is observed substantially asdescribed in Example 1. After about 35 minutes from the onset of thethick paste state in the reaction mass, about 62 g. of vinyl chloridemonomer (corresponding to about 8.6% based on the net charge of vinylchloride monomer) is vented from the reactor over a period of about 10minutes (corresponding to an average rate of vinyl chloride removal ofabout 0.86 percent per minute) following the venting procedure describedin Example 1. On completion of the venting operation the reaction iscontinued at about the aforementioned conditions of temperature,pressure and agitation with the effective polyolefin concentration beingabout 9.1% (based on the net vinyl chloride charged less the vinylchloride vented). After about 15 minutes subsequent to completion of theventing operation, the reaction pressure drops indicating the completionof the polymerization as in Example 1. Following the procedure ofExample 1 residual vinyl chloride is vented from the reaction vesselwhich is allowed to cool to ambient temperature. The reaction product isrecovered from the reaction vessel and the reactor agitatorsubstantially as described in Example 1.

The product which is characterized by excellent properties substantiallysimilar to those of the Example 1 product consists of a particulatepolymer fraction (240 g.) and a non-particulate fraction composed ofscrapings from the agitator and reactor (substantially no reactor walldeposit is present) amounting to 26 g. (corresponding to about 9.8% ofthe total product). The total yield of product amounts to 266 g.(corresponding to a conversion of about 29% of the net charge of vinylchloride monomer to polymer) of which about 22.6% is polyolefin.

The particulate portion of the product is passed through a No. 16 meshsieve (aperture size about 1.2 mm) as in Example 1. The amount ofparticulate polymer which passes through the No. 16 mesh sieve, i.e.product particles of average cross-sectional width of about 1.2 mm orless is about 60 g. (about 22.5% of the total product). The amount ofparticulate polymer retained on the No. 16 mesh sieve, i.e. polymerparticles of average cross-sectional width greater than about 1.2 mm is180 g. (about 67.7% of the total product). Of the particles retained onthe No. 16 mesh sieve, the two largest particles have an averagecross-sectional width of about 10 mm, the next 15 largest particles havea cross-sectional width of about 5 mm and the remaining particles have across-sectional width of less than about 5 mm.

The foregoing product fraction which is retained on the No. 16 meshsieve is further sieved through a No. 10 mesh sieve (aperture size about2 mm). The amount of these product particles which is retained on theNo. 10 mesh sieve, i.e. particles of average cross-sectional widthgreater than about 2 mm, is about 96 g. (corresponding to about 36.1% ofthe total product). The amount of these product particles which passesthrough the No. 10 mesh sieve is about 84 g. so that the combined amountof product particles which pass through the No. 16 mesh sieve and theNo. 10 mesh sieve, i.e. product particles having an averagecross-sectional width of about 2 mm or less, is about 144 g. (about 54%of the total product).

The foregoing results of Example 10 are summarized in Table II below.

EXAMPLE 11 (CONTROL)

The polymerization procedure of Example 10 is repeated substantially asdescribed except that the venting of vinyl chloride monomer during thethick paste state of the polymerization is omitted.

The polymer product is recovered after polymerization for about 5.5hours and is examined for particle size distribution substantially asdescribed in Example 10. The results of this control example aresummarized and compared with the results of Example 10 in Table IIbelow.

                                      TABLE II                                    __________________________________________________________________________         Net                                                                           Vinyl               Effective     Time of Beginning                                                                       Duration                                                                            % Conversion                Chloride                                                                           % Vinyl Chloride                                                                       %     % Con- Rate   of Venting After                                                                        of    of Vinyl Chlo-              Charged                                                                            Vented During                                                                          Polyolefin                                                                          centration of                                                                        of Venting                                                                           Inception of Thick                                                                      Venting                                                                             ride (Duration         Example                                                                            (g.) Thick Paste State                                                                      Charged                                                                             Polyolefin                                                                           (% per min.)                                                                         Paste State (min.)                                                                      (min.)                                                                              of                     __________________________________________________________________________                                                           Reaction)              10   720  8.6      8.3   9.1    0.86   35        10    29 (4.4 hrs.)          11   720  none     8.3   8.3    0      --        0     37 (5.5 hrs.)          (Control)                                                                     __________________________________________________________________________                                          Particulate Product                                % Total Product                                                                        % Total Product                                                                        % Total Product                                                                        % Total Product                              % Total                                                                             ≦About 1.2 mm                                                                   >About 1.2 mm                                                                          ≦About 2 mm                                                                     >About 2 mm                                                                             Largest                                                                                % Non-le                  Polyolefin                                                                          Cross Sectional                                                                        Cross Sectional                                                                        Cross Sectional                                                                        Cross Sectional                                                                         Size in                                                                                % Particulate        Example                                                                            in Product                                                                          Width    Width    Width    Width     Product                                                                                Product              __________________________________________________________________________    10   22.6  22.5     67.7     54.2     36.1      10 (2 particles                                                                         9.8*                                                                this size)                    11   18.3  10.7     77.4     24.1     65.8      40-50 (5-10                                                                            11.9**               (Control)                                       particles this                __________________________________________________________________________                                                    size)                          NOTES:                                                                        *contains reactor bottom cake, and scale deposit on stirrer; no reactor       wall scale formed                                                             **contains reactor bottom cake scale and deposit on stirrer together with     reactor wall scale (18% on the weight of the nonparticulate product           fraction)                                                                

In the foregoing Examples 1, 3-5, 7, 8 and 10 which are illustrative ofthe invention it will be apparent that many process changes can be madewithout departing from either the spirit or the scope of the invention.For example, if desired, a portion, e.g. about 10% of the vinyl chloridereactant, may be replaced by a compatible comonomer, e.g. methylacrylate, to obtain an excellent finely divided particulate vinylchloride-methyl acrylate-polyolefin polymer. Also, advantageously thevinyl chloride which is allowed to escape in the aforementionedillustrative examples can be collected by venting the vinyl chloride toa cooled receiver at atmospheric pressure or to a compressor forliquification. The resultant recovered vinyl chloride can be reservedfor later polymerization. Furthermore, excellent results are obtained inthe aforementioned illustrative examples when the ethylene propylenepolyolefin reactant is replaced by the following olefin polymers:polyethylene, polypropylene and ethylene propylene diene-modifiedterpolymer having an ethylene/propylene ratio of 55/45 and containing1,4-hexadiene as the diene in an amount of 3±0.5 percent, a1-buteneethylene copolymer containing 5% ethylene and chlorinatedpolyethylene sold under the trademark "Tyrin".

Moreover, instead of adding the polyolefin reactant directly to thepolymerization as described in the above Examples, the polyolefin can bemixed with all, or more conveniently, a portion of the vinyl halidemonomer reactant and dissolved, partially dissolved or dispersed in saidmonomer with heating and/or agitation, as desired, prior to addition tothe reaction vessel. While the addition of the polyolefin to thepolymerization reaction mixture according to the invention can becarried out at the beginning of polymerization reaction, i.e. at 0%conversion by weight of monomer to the polymer, it is desirable that thepolyolefin be added immediately after some of the monomer, i.e. up toabout 20%, has been converted to polymer, preferably after about 1% toabout 15%, more preferably about 3% to 15% conversion of monomer topolymer. When the polymerization is operated as a two stage process inaccordance with the aforementioned techniques of British Pat. No.1,047,489 and U.S. Pat. No. 3,522,227, the polyolefin is added to thepolymerization substantially immediately after the completion of thefirst stage, i.e. after preferably about 3% to 15% by weight and morepreferably about 7% to about 15% of the monomer has been converted topolymer. Conveniently, in carrying out the polymerization in the twostage reaction configuration, the polyolefin is added to the secondstage so as to be present in the second stage reaction vessel prior tooccurrence of any substantial polymerization therein.

The addition of the polyolefin reactant subsequent to initiation of thepolymerization as described above provides in conjunction with themonomer venting procedure of the invention, in general, a fasterpolymerization reaction, a lower concentration of residual vinyl halidemonomer in the polymerization product, and especially, a particularlyexcellent distribution of product particle size, i.e. the product ischaracterized by an especially narrow distribution of product particlesize and contains an especially large, generally predominant, fractionof the most minute particles. Such improved product particle sizedistribution is of especial advantage in many uses of the product suchas injection molding and extrusion of articles such as pipe and siding.

According to another preferred mode of carrying out the invention, it isadvantageous when operating the polymerization according to theaforementioned two stage configuration to add to the first reactionstage only a portion, of the monomer or monomers used in the processwith the balance being added so as to be present in the second reactionstage prior to the thick paste state venting operation which in the twostage reaction configuration is carried out in the second reactionstage. Generally at least about 50% by weight or more of the monomerreactant (corresponding to at least about 60% by weight or more of themonomer reactant when the amount of monomer vented in the thick pastestate is discounted from the amount of monomer used in thepolymerization) is added to the first reaction stage with the balancebeing added at about the beginning of the second reaction stage (so thatit is present prior to the venting operation of the invention).Preferably about 50% to about 60% by weight of the monomer reactant isadded in the first reaction stage (corresponding to addition of about60% to about 70% of the monomer reactant when the monomer reactant whichis vented is discounted as described above).

This preferred mode of charging monomer or monomers in carrying out thepolymerization in the aforementioned two reaction stage configurationpermits use of a first stage reaction vessel of smaller size than thatused in the second reaction stage and also in general, assists inproviding a product of excellent particle size distribution.

While this invention has been described with reference to certainspecific embodiments, it will be recognized by those skilled in the artthat many variations are possible (as illustrated above) withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A high impact strength vinyl halide polymer ofimproved small particle size prepared by the improved process whichcomprises polymerizing in bulk a vinyl halide monomer, in the liquidphase, either alone or in combination with up to about 50% by weight ofanother ethylenically unsaturated monomer copolymerizable therewith, inthe initial presence of more than about 1.8% by weight based on saidvinyl halide monomer of a polyolefin or mixture of polyolefins having aweight average molecular weight of about 50,000 to about 1,000,000,wherein the improvement in said process comprises removing from thepolymerization mass during the thick paste state thereof from about 2%to less than about 50% by weight of the vinyl halide charged to thepolymerization mass, the effective concentration of said polyolefin ormixture of polyolefins after said vinyl halide removal being above about3.5 weight percent based on vinyl halide remaining in saidpolymerization mass after said removal of vinyl halide whereby a morefinely divided particulate product of high impact strength is obtained.2. The product of claim 1 wherein the weight average molecular weight ofthe polyolefin reactant is about 50,000 to about 150,000.
 3. The productof claim 1 wherein the weight average molecular weight of the polyolefinreactant is about 150,000 to about 1,000,000.
 4. A high impact strengthvinyl halide polymer of improved small particle size prepared by theimproved process which comprises polymerizing in bulk a vinyl halidemonomer, in the liquid phase, either alone or in combination with up toabout 50% by weight of another ethylenically unsaturated monomercopolymerizable therewith, in the initial presence of more than about1.8% by weight based on said vinyl halide monomer of a polyolefin ormixture of polyolefins having a weight average molecular weight of about50,000 to about 1,000,000, said polyolefin or mixture of polyolefinsbeing present during the polymerization only during the period whichcommences at 0% to about 20% conversion of the monomer or monomers topolymer and concludes with the end of the polymerization, wherein theimprovement in said process comprises removing from the polymerizationmass during the thick paste state thereof from about 2% to less thanabout 50% by weight of the vinyl halide charged to the polymerizationmass, the effective concentration of said polyolefin or mixture ofpolyolefins after said vinyl halide removal being above about 3.5 weightpercent based on vinyl halide remaining in said polymerization massafter said removal of vinyl halide whereby a more finely dividedparticulate product of high impact strength is obtained.
 5. A highimpact strength vinyl halide polymer of improved small particle sizeprepared by the improved process which comprises polymerizing in bulk avinyl halide monomer, in the liquid phase, either alone or incombination with up to about 50% by weight of another ethylenicallyunsaturated monomer copolymerizable therewith in the initial presence ofmore than about 1.8% by weight based on said vinyl halide monomer of apolyolefin or mixture of polyolefins having a weight average molecularweight of about 50,000 to about 1,000,000, said polyolefin or mixture ofpolyolefins being present during the polymerization only during theperiod which commences at 0% to about 20% conversion of the monomer ormonomers to polymer and concludes with the end of the polymerization,said polymerization being carried out in a first stage wherein thereaction mixture is subjected to high speed agitation until about 3% toabout 20% by weight of said monomer or monomers have been converted topolymer, and further polymerizing the resultant reaction mixturetogether with additional monomer or monomers in a second stage duringwhich the reaction mixture is subjected to low speed agitation until thepolymerization has been completed, wherein the improvement in saidprocess comprises removing from the polymerization mass during the thickpaste state thereof from about 2% to less than about 50% by weight ofthe vinyl halide charged to the polymerization mass, the effectiveconcentration of said polyolefin or mixture of polyolefins after saidvinyl halide removal being above about 3.5 weight percent based on vinylhalide remaining in said polymerization mass after said removal of vinylhalide whereby a more finely divided particulate product of high impactstrength is obtained.